DE-C-531,382 describes a dressing apparatus with a dressing chamber, in which a jet of dressing is generated radially from a centrifugal disk outwards and is sprayed two-dimensionally. A continuous veil of seed falls down outside the centrifugal disk over the entire periphery, and the seed and jet of dressing meet one another along a circular line. Such an arrangement has not always proved entirely satisfactory, especially because some of the dressing settles on the walls of the apparatus and the seed grains can therefore never be enveloped to a sufficient extent.
In contrast to this, in the state of the art known from HU-A-157,922, the functions are partially reversed. Here, the product stream is thrown off in freefall onto a conical centrifugal grain plate arranged inside a dressing chamber. The free-falling stream of grains is acted upon over the entire length of its travel by two spray nozzles located opposite one another. The grain stream is deflected by means of the centrifugal grain plate and the retention time of the individual grains in the dressing space is increased, thus improving the mixing of the grains with the dressing.
However, the disadvantage of the two above-indicated solutions from the state of the art is that a considerable proportion of the dressing is sprayed onto the wall of the apparatus located opposite the dressing nozzle, and this is no longer desirable, especially where the mercury-free dressings used more and more frequently are concerned, since these dressings are sometimes extremely sticky and can form crusts on the walls of the apparatus. Furthermore, as can quickly be established by means of dressing patterns, the known apparatuses unfortunately do not ensure that the dressing is sufficiently distributed over the grain as desired, and even the distribution intensity varies greatly from grain to grain. When mercury-containing dressings were used, this was not so important because it was still possible to obtain via the evaporation stage a relatively uniform covering over all the grains, even in the bags filled for the user. This is because, as a result of the mercury vapor pressure, the substances diffuse in gas form more easily into the places on the grain, even into uneven regions and, for example, into the grain furrow, so that it was thereby possible to cover relatively effectively even hollow places with a protective layer via tiny crack orifices in the furrow region. More recently, however, new trends among users have become noticeable. One of these arises because the dressing is intended to exert a so-called aureola effect in the soil, that is to say some of the dressing on the grain sown in the soil dissolves, diffuses into the immediate vicinity and kills troublesome microbes and fungi in the soil within a certain circumference. A complete and uniform covering with dressing is not absolutely necessary for this. However, objections to the effect that this method should preferably not be used for seed have been raised more recently on ecological grounds.
In some countries, the use of mercury for dressings is prohibited because of the toxicity of mercury, so that new solutions have to be sought from both the chemical and the constructive point of view, so that at the very least the quantities of poison required can be kept as low as possible.
Starting from this, the object on which the invention is based is to develop a seed dressing process which produces an excellent dressing effect, whilst at the same time ensuring a particularly low consumption of dressing, and also to find an apparatus which is especially suitable for this.
According to the invention, in a process of the type mentioned in the introduction, this is achieved because the seed is thrown off in dispensed doses as a free-falling annular veil into a trough-shaped rotary table, and during its freefall is guided through a two-dimensional jet of dressing thrown outwards from the interior of the annular veil, and subsequently the wetted seed is subjected to a dressing again on the rotary table during throwing out, the dressing being finely distributed on and massaged into the surface of the grains because the individual seed grains roll on the rotary table continuously and simultaneously come up against one another and rub on one another.
In the process according to the invention, a particularly intensive dressing effect is obtained because the seed streaming down in the manner of a veil is coated very intensively and uniformly over the grain surface as a result of the annular jet of dressing effective in two dimensions and of the wetting surface which is relatively large due to the annular veil. The seed wetted in this way then falls down onto the trough-shaped rotary table and there is accelerated radially outwards, continually changing its position, the dressing present on the surface of each grain thereby being distributed even more uniformly over the surface. During this throwing-out operation, the seed wetted in this way is sprayed with dressing again, that is to say "for the second time", thus providing a second wetting operation which lags a certain time behind the first wetting operation in the falling annular veil. This second later wetting operation starts precisely at a moment at which not only was the first wetting operation already concluded (as regards the supply of dressing), but the dressing coated on the particular grain surface during the first wetting operation had even then already been further distributed and made uniform there as a result of the impact of the grain on the rotary table and the subsequent centrifugal effects. The second wetting operation then takes place in this situation, and for this the initial conditions for a further absorption of dressing on the grain surface are thus particularly favorable. However, because the centrifugal action is still taking place at the same time on the rotary table, the dressing supplied later is also distributed over the surface of the seed grains immediately and in a particularly effective way, and consequently the seed grains, when they leave the centrifugal plate, have in the end an especially good and uniform distribution of dressing on their surface.
It has emerged that the triple effect achieved by means of the invention, namely
(1) a first spraying of an annular grain veil, PA1 (2) a drum-like incorporation, mixing and rubbing of the predressed grain on a trough-shaped rotary table, and PA1 (3) a subsequent intensive dressing of the seed on the rotary table,
leads to surprisingly good results. At the same time, a multiplicity of force effects can be exploited. Because of the relatively high speed at which the grain can rotate about all the possible axes and move in very many directions in space, strong twisting movements of the grain can be achieved, the result of this being that the drops of dressing sprayed on are rapidly distributed over its surface and even penetrate in a similar way to a "creeping oil" into depressions and cavities which can only be reached via fine orifices, and are thereby distributed very finely. As a result of the strong movement of the grains and the intensive impact and frictional forces between the grains and relative to the trough-shaped rotary table, the grains equalize between them the amount of dressing on them, thus resulting in a massaging process on the grain surface.
The invention permits various other preferred embodiments:
It is especially preferred if the jet of dressing delivered two-dimensionally is thrown out in the form of an atomized dressing, for example via a centrifugal plate rotating at high speed about a vertical axis and via a strong airflow for atomization. This results in particularly good alignment and controllability of the dressing with regard to the moving seed streaming down in the manner of a veil, thus also improving the self-cleaning of the apparatus.
The apparatus according to the invention starts from an apparatus of the type mentioned in the introduction and is defined in that the rotary table is made dish-like with an edge extending upwards and outwards, a dressing spray device being arranged concentrically relative to the rotary table, and there being attached above both of these a seed dispensing and distributing channel, via which the seed streams down onto the rotary table in the form of an annular veil.
It is possible by means of the apparatus according to the invention to dress the indivioual seed grains very intensively, using markedly less dressing in comparison with known apparatuses, without the germinating capacity of the seed being impaired or grain damage or grain breakage occurring.
In an advantageous embodiment of the apparatus according to the invention, the rotary table and the dressing spray device have a form similar to one another (for example, a circular form) and are preferably designed with a flat central region.
In a further especially advantageous embodiment, the rotary table recessed in the manner of a dish terminates in its edge region obliquely relative to the horizontal, preferably at an angle of at most 75.degree., but especially at an angle of between 30 and 75.degree., the inclination being selected especially between 55.degree. and 65.degree., for example below 60.degree.. In an apparatus according to the invention, it is also advantageous to attach a guide device for the seed above the dish-like rotary table, as a result of which the seed streaming down in the manner of a veil can be aligned in its stream path in such a way that it strikes a predetermined region of the rotary table, especially its region of transition from the flat central part to the edge extending upwards. A particularly preferred embodiment for this is designed so that the guide device has a seed distributor cone which is arranged coaxially relative to the geometric axis of rotation of the rotary table and via which the seed flows down. It is also highly advantageous if the guide device has, underneath the distributor cone and radially outside the latter, an especially cylindrical guide wall opposite which is located, again preferably, a radially inner wall parallel to it. Advantageously, the dressing spray device is arranged on the side of the guide device facing away from the seed feed, especially on the underside of the distributor cone, and is closed off and covered over by this. Preferably, the distributor cone is also adjustable relative to a common guide surface forming an annular gap with the cone surface, in order to adjust the size of the gap, and for this purpose it can be connected, for example, to a remotely controllable adjusting device. At the same time, the distributor cone can preferably be arranged on an advantageously hollow column which is connected to the adjusting device and which receives the feed device for the dressing.
A particularly advantageous overall effect is obtained when the dressing spray device is designed as a high-speed pneumatic motor, the rotor of which has a working speed in the range of preferably 5,000 to 20,000 revolutions per minute, and at the same time the motor exhaust air can be used for atomizing (spray formation) the jet of dressing.
In a further advantageous embodiment of the apparatus according to the invention, the dressing spray device preferably having a centrifugal plate and/or at least one nozzle is arranged in such a way that the impact region of the jet of dressing (used for the second repeated supply of dressing) on the rotary table is arranged not in its central region, but at a distance from this. At the same time, the centrifugal plate is preferably arranged at half the height over which the edge of the dish-like rotary table extends upwards, in an at least approximately horizontal plane and concentrically relative to the rotary table.
As regards the operating reliability of the apparatus as a whole, especially good results can be achieved if the centrifugal plate is driven by a pneumatic motor, the exhaust air of which can be fed to the nozzle for spraying out the dressing, to obtain an injector effect. It is advantageous, furthermore, if there is a device by means of which the speed of the rotary table can be adjusted. The dressing spray device preferably has a pump which delivers the jet of dressing from its rotor and which is preferably designed as a radial pump (especially resembling a centrifugal plate), and the rotor of this radial pump appropriately has edge blades arranged obliquely relative to the radial direction. The dressing spray device is also preferably provided with an injector channel for feeding air to at least one dressing nozzle or for atomizing the dressing, and advantageously an atomizing chamber is formed in the region where the air and dressing meet.